Description: The lifespan of an individual flower is often affected by pollination success. Species differ regarding whether male function pollen removal, female function pollen deposition, or both trigger floral senescence. We studied senescence in the single- flowered, deceptive orchid Calypso bulbosa by manipulating the degree of male and female reproductive success. We found that deposition of any amount of pollen resulted in dramatic changes in shape and color within 4 d, whereas unmanipulated flowers and those that had had pollinia removed remained unchanged for 8-11 d after treatment. Selection may favor the reproductive function that is less easily satisfied as the trigger for senescence, because a flower that senesces after accom- plishment of this function is likely to have already succeeded at the more easily satisfied one. Deceptive i.e., rewardless flowers are more likely to satisfy male than female function since the latter requires that a pollinator be fooled twice, first to pick up pollen and second to deposit it. A survey of naturally pollinated Calypso showed that male function, pollinium removal, was more likely to occur than female function, deposition 95% vs. 66% of visited flowers; thus floral senescence in Calypso is triggered by achievement of the function less likely to succeed. Studies of senescence triggers in species in which female function is more likely to be achieved than male are necessary to further test this hypothesis.

Date created: 1995

DOI: doi:10.7939-R3WW0W

License information:

Rights: This version of this article is open access and can be downloaded and shared. The original authors and source must be cited.